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Hi! I'm using an Apple Wired Keyboard on my 2013 MBP. The keyboard came with my previous iMac. It is connected directly to my Mac, and there's a Logitech mouse connected in one of its USB port. When I plug my iPhone 6 into the other port, the iPhone will act as it has been disconnected and reconnected (screen comes on and it makes a sound) and while this happens, my mouse and keyboard will stop working for a few seconds, as if the keyboard was rebooting. My cursor will stop moving and the letters typed won't register. It does this every few seconds so it's really annoying. Any idea? There has never been any damage to the keyboard and nothing spilled on it. It doesn't matter what combinaison of ports I use.

Probably the keyboard doesn't supply enough power to actually charge the phone, and since the phone won't trust a computer as its host until you press that button the display, it keeps disconnecting and reconnecting. What happens if you press the button on the phone to allow the computer to access it?

I really wish OS X was better about displaying messages about USB problems due to insufficient power. I thought it used to say something about this. But P's answer is correct. There's no way the keyboard can supply enough power to charge the phone, which is what the iPhone is expecting, so the USB bus is continuously getting reset. Either connect the phone directly to the computer or to a powered USB hub.